The present invention relates to an optical information recording medium capable of recording information thereon by the application of high density energy beams thereto, the recorded information being thereafter reproducible therefrom, which optical information recording medium comprises a base and an improved information recording layer thereon, in which recording layer the recording is done by causing a change of state of the materials contained in the recording layer, such as a change in reflectance and/or in light transmission caused by fusing, vaporization, sublimation or other phase transformations, as the high density energy beams are applied thereto.
In the optical recording of information, a laser beam, for instance, is applied in image patterns or code patterns to a recording layer of an optical information recording medium, so that the laser beam is absorbed by the recording layer. The light energy imparted by the laser beam is converted to thermal energy within the recording layer. By the converted thermal energy, the materials contained in the recording layer are subjected to the above-mentioned changes of state in the image or code patterns so as to record the information in the recording medium.
In conventional optical information recording media, from which reading or reproduction of the recorded information is done by the so-called reflection method, the recording layer of the medium comprises a light-reflecting material, for example, aluminum or gold, coated with a light-absorbing material. By application of the laser beam, the light-absorbing material is vaporized and the underlying reflective material exposed. Thereafter, in the reproduction of the recorded information, a laser beam which is less intense than the laser beam employed for the recording is applied to the surface of the recording layer, and the difference in reflectance between the exposed light-reflecting material in the recorded areas and the non-reflective light-absorbing material in non-recorded areas is detected. From this detection, the recorded information is reproduced.
However, the use in those recording media of the aforementioned light-reflecting layer, formed separately from the coating of the light-absorbing material, makes the production process rather complex and the production cost high.
Moreover, those recording media (for instance, those disclosed U.S. Pat. No. 4,241,355 to Bloom et al. and Japanese Laid-Open Patent Application No. 55-97033) do not possess the high laser-beam absorption efficiency that would permit their use with semiconductor lasers, that is, cannot absorb wavelengths above 780 nm, although semiconductor lasers would themselves be extremely advantageous in terms of their lightness in weight, smallness in size and other practical advantages. Instead, with those recording media, high-cost, high-power lasers must be used.
Thus, what was lacking in the art heretofore was an optical information recording medium simple and economical to produce, which is efficient is absorption of laser beams of wavelengths of 780 nm or more (i.e., provides good recording efficiency), particularly beams from a semiconductor lasers, and which, after recording, exhibits high reflectance contrast between the recorded areas and the adjacent non-recorded areas (i.e., provides good reproduction performance).